A living body produces and releases a lot of life information all the time. The life information may be summarized into two categories: chemical information (chemical components that constitute the living body and information relating to its changes) and physical information (shapes, locations, relative relationships of organs in the living body, and force, heat, sound, light, and other related information generated by movement of the living body). A circulatory system formed by Heart and vessels of some animals may constitute a blood circulation and may be one of the most important organs and components for the animals. The chemical information and physical information of a cardiovascular system contains a large amount of information about health of the animals. Among them, one of the main techniques applied to diagnosing heart conditions and performances is electrocardiogram (ECG). The ECG records the surface potential difference produced during the beating of the heart. In 1903, Einthoven, a professor of physiology in Leiden University in the Netherlands, measured the ECG using a string electrometer manual. In addition, an animal body pulse system is an important component of the cardiovascular system and an important way to transport nutrients and transfer energy. A pulse comes directly from the heart and is a fluctuation caused by the contraction of the heart. A left ventricle injects blood into an aorta through an aortic valve, causing a pulsation of flow, pressure, and diameter in the arterial tree. One of the important life information generated by the pulse system is photoplethysmography (PPG). The propagation characteristics of the PPG are closely related to the changes of mechanical parameters in the cardiovascular system and the PPG includes a lot of physiological information of the animal body. In 1860, Vierordt, a Frenchman, developed the first spring lever-type pulse tracer to obtain a pulse wave waveform.
The measurement of the PPG or the measurement of the ECG may be effected by noises, artifacts, and data loss, which may result in a wrong analysis result. Generally, the following common noise interference may exist in collected signals: baseline drift, power frequency interference, electromyographical interference, and motion/vibration interference. The baseline drift is caused by a poor contact of clicks and impedance changes on the electrode-skin interface of a subject. The baseline drift is a low frequency interference signal and the frequency is generally less than 1 Hz. The power frequency interference is generated because that a distribution capacitance on human body and a lead loop of click electrode are affected by an alternating current and a magnetic field. The frequency of the power frequency interference is 50 Hz frequency and its harmonics. The electromyographical interference is caused by body jitter and muscle tension. The frequency of the electromyographical interference is relatively large. The motion/vibration interference may refer to that during the signal input process, a signal generator (e.g., a transmission distance of a light source, a transmission angle of the light source) may change due to movement or vibration of the subject, the light source, or the sensor, and therefore, the signal characteristics are affected and the signal may be disturbed, distorted, or submerged.